THE INITIATION, SIGNIFICANCE AND DETECTION OF BURIED LAMELLAR TEARS IN WELDED TEE JOINTS

The present study was aimed toward (1) the resolution of uncertainties about lamellar tearing initiation temperatures, (2) the evaluation of the significance of buried lamellar tears on the load carrying capacity of welded tee joints in tension, bend, and fatigue loading and (3) development of reliable ultrasonic testing technique to detect buried small tears.; In order to measure the lamellar tearing initiation temperature, the slice bend test was conducted at elevated temperatures on A572 Grade 50 and A588 Grade A steels and a test was devised for tear initiation temperature measurement with A572 steel. In slice bend tests A572 steel showed the most susceptible region to lamellar tearing to be in the range of 100 to 300C, where the steel showed the minimum ductility. In static loading of two steels, the load carrying capacity was significantly reduced when the tear intercepted over 10% of the cross-sectional area of the welded joints.; Fatigue strengths of welded joints containing tears near the weld toe were markedly reduced with increasing tear areas while lamellar tears located away from the weld toe did not reduce the fatigue strength and performed like tear-free welded joints. The load carrying capacity in static loading was influenced by the reduction of supporting area.; In bend tests, the pre-existing lamellar tears always grew up toward the weld toe. In fatigue loading, delaminations and decohesions of inclusion/matrix interfaces generated in multipass welds provided crack paths and enhanced crack propagation because the tips of delaminations and decohesions acted as stress raisers.; The detection of tears by the straight-beam contact test was confirmed by slicing to produce the accurate measurements of tear area, morphology, tear height and length. A large proportion of incident beam was reflected to the transducer because the terraces of lamellar tearing were essentially normal to the incident beam.; The minimum size of buried lamellar tears detected by UT was 2mm. Undetected tears tended to be tight, discontinuous cracks which did not reflect a large proportion of the incident ultrasound beam. An undetected tear only 2mm wide would not reduce the load carrying capacity in static loading regardless of its length. (Abstract shortened with permission of author.)...